Flash memory is a form of electrically erasable programmable read only memory (EEPROM). Unlike typical EEPROM, which is erasable one byte at a time, flash memory is capable of being erased one block at a time. Block sizes vary for various flash memory devices. Flash memory devices are typically small, light weight, and consume low amounts of power. Thus, flash memory is appropriate for devices such as mobile devices, battery powered devices, devices desiring low power consumption, and/or small devices, for example. Two popular types of flash memory are NOR flash memory and NAND flash memory. As the names suggest, NOR flash memory utilizes circuitry comprising NOR gates and NAND flash memory utilizes circuitry comprising NAND gates.
NAND flash memory has several advantages over NOR flash memory. NOR flash memory is less dense than NAND flash memory. That is, more bytes of memory can be incorporated into a volume of NAND flash memory than can be incorporated into the same volume of NOR flash memory. The access times associated with NOR flash memory are typically slower than access times associated with NAND flash memory. Further, development costs associated with NAND flash memory are typically less than development costs associated with NOR flash memory. Thus, it would appear that NAND flash memory would be the obvious choice for any application.
However, NAND flash memory has a disadvantage which, to date, has limited its use. NAND flash memory is prone to developing bad blocks of memory. Two primary occurrences of this are often observed. One observance is that blocks within a NAND flash memory device are bad when the NAND flash memory device is delivered from the manufacturer. The other is that blocks go bad while the NAND flash memory device is being used. The latter is often due to a NAND flash memory device's fixed write/erase endurance.
There is a desire to utilize NAND flash memory while mitigating the above detrimental effects.